The simplest way to create a schema is to pass JSON data directly to JsonSchema.createSchema with a JSON String, or decoded JSON via Dart Map or bool.

After creating any schema, JSON instances can be validated by calling .validate(instance) on that schema. By default, instances are expected to be pre-parsed JSON as native dart primitives (Map, List, String, bool, num, int). You can also optionally parse at validation time by passing in a string and setting parseJson: schema.validate('{ "name": "any JSON object"}', parseJson: true).

Note: Creating JsonSchemas synchronously implies access to all $refs within the root schema. If you don't have access to all this data at the time of the construction, see "Asynchronous Creation" examples below.

If you want to create JsonSchemas synchronously, and you have $refs that cannot be resolved within the root schema, but you have a cache of those $ref'd schemas locally, you can write a RefProvider to get them during schema evaluation.

If you have schemas that have nested $refs that are HTTP URIs that are publicly accessible, you can use Future<JsonSchema> JsonSchema.createSchemaAsync and the references will be fetched as needed during evaluation. You can also use JsonSchema.createSchemaFromUrl if you want to fetch the root schema remotely as well (see next example).

Schema information can be used for validation; but it can also be a valuable source of information about the structure of data. The JsonSchema class fully parses the schema first, which itself must be valid on all paths within the schema. Accessors are provided for all specified keywords of the JSON Schema specification associated with a schema, so tools can use it to create rich views of the data, like forms or diagrams.

One example use is the deprecatedschemadot program included in the bin
folder which takes schema as input and outputs a Graphvizdot
file, providing a picture of the schema. This does not provide all
information of the schema, and is a work in progress - but it can be
useful to see what a schema is.